Arrangement for starting and regulating direct-current electric motors



. F. CUMONT. ARRANGEMENT FOR STARTING AND REGULATING DIRECT CURRENT ELECTRIC MOTORS.

' APPLICATION FILED APR. 1, 1913. 5 1,41 1,419. I Patented Apr. 4, 1922 3 SHEETS-SHEET I- I N IVE Er .W'IFBsses -F. CUMONT.

ARRANGEMENT FOR STARTING AND REGULATING DIRECT CURRENT ELECTRIC MOTORSI APPLICATION FILED APR. II 1913- Patented Apr. 4, 1922,

acumom. ARRANGEMENT FOR STARTING AND REGULATING DIRECT CURRENT ELECTRIC MOTORS.

APPHCATION FILED APR. 1, I913. 1,411,41 9. Patented Apr. 4, 1922.

3 SHEETSSHEET 3- of winding.

UNITED STATES ,PATEN'T OFFICE.

FERNANI) contour, or r'Anrs, FRANCE, ss enofn 'ro 'socrntrn nr'i ns r. A. 3/ (SYSTEME nn TRACTION AUTO-REGULATEUR), or PARIS, FRANCE.

ARRANGEMENT FOR, STARTING- AND anen'na rrim nmno'r-ct'r'nnnnr ELECTRICL MOTORS. 7

. Specification of Letters Patent. 7

Application filed April 1, 1918. 5eria1"No.758,"212.

(GRANTED UNDER THE PROVISIONS or. THE Act or MARC 3,-1921;41 s'rArsL, 1318.)

To all to 7mm it may concern: v

Be it known that I, FERNAND CUMoNr, a citizen of the Republic of France, residing in Paris, in the Republic of France, have invented certain new and useful Improvements in Arrangements for Starting and Regulating Direct-Current Electric Motors, of which the "following is a specification.

The invention relates to improvements in connection with arrangement for producing in an entirely automatic manner the starting speed regulation and regenerativerunning of continuous current electric motors in which a special electric machine takes in or gives out a current of constant strength. This is insured by driving the machine at a constant speed and allowing ittobe acted upon byttvo fluxes,'one oi which is of constant value, while the other is proportional in value .to the voltage across the brushes 0'? the mael'iine. The improvements will be better understood by referring to the draivings herewith in which 1- Figurel is a diagram showing the characteristics'ot the above mentioned machine,"

Figure 2 is a diagram "for a similar ma-,

chine worlzin inthe saturatedportion of.

its characteristic. 7

; Figure 3 is a. similar" diagram for the case in which. the current passing through the machine varies according to a predetermined. law.

Figure 4ishoWs a method'of applying the machine to system of traction motors in series provided with a special arrangement Figure fi shows the replacement of the windingsof the said machine by a single Winding excited by a small dynamov Figureso and 7 7 show different methods for producing the establishment and the stabilizing of the braking.

Figure 8 shows the application of above improvements to a. traction system with means for regulating and controlling same.

Referring to Figure l-the line 0 B represents the open circuit characteristic of the machine as Well as thecharacteristic of its shunt Winding. If this machine operates or Works in the non-saturated portion of its magnetic circuit the current which passes through it is measured by the line- C "D n hichcorresponds to tail of voltage in the armature otythe machine, If the chine Worksinthe saturated portion of its magnetic circuit (seeFigure 2) thewcharaew teristic of the shunt Windin'gO Swill separate from the'open circuit characteristic 0 R of the machine and in consequence the current will then be measured by'the line C D which is greater than Cl). Under ,these 'condi-r tions the current absorbed by the machine,

brushes. 1 i i In the case in which will increase with the voltage across its Because of these properties it *is'ipossible,

for. example, to leave this special machine constantly in clrc'uit (hiring the starting of the traction motors. p i M order to make the current absorbed or given out follow a" predetermined law it is sufficient that-the characteristic of the shuntexcitation, for example, S (Figureii) should no longer coincide with'the open circuit characteristic 0 B of the machine.

The lines E Z and F GRvhi'c'h representthe resultant characteristic of the excitation windings of the machine acting as a generator or motor respectively which lie parallel to O S can be used to determine the value. of the current passing through the machine.

The line '0 S"could also be inclined in the direction 0' S Under theseico'nditions the machine is capable oi automatically starting'and braking the motors with a continuously increasing or in decreasing current or at least as long'as the machine works in the non-saturated part of its magnetic characteristici" When the sat urated partis reached the influence of'the machine is identical With-that ivliich'has been referred to'fpreviouslm that is to say if it'is functioning as a motor the current ab sorbed increases with the voltage applied to its terminals, Whilstif *it is functioningas a the machine is func tiomng-as a generator the line representing manna. A r. 4,1922.

generator the current sent out by it diminishes. It is obvious that this machine could be used for any case in which these properties are specially useful.

Referring to Figure 4 e F 6 represents the regulating machine having windings E, E and L. These are shown connected with two series traction motors M and M In this case theinachine F is used for maintaining the current through the traction motors at constant value while working below the limits of saturation. In order that this may be understood it will be noted that the winding E is placed across the terminals of the traction motor M, the winding E is placed across the terminals of the traction motor M and consequently the excitation of these windings depends on the voltage across the motors. The third winding L is placed directly across the mains and may be considered as being compounded of two constant factors, one of which may be designated by the letter K and the other by the letter H which latter is an opposing excitation due'to the current passing through the machine so that the total effect of the wind ing L will be equivalent to the effect of K less the effect of H. Now all these windings have a certain effect on the exeiter F and if suitably designed each winding will tend to produce when the machine is working in a non-saturated portion of its characteristic a voltage equal to that which is across the winding in question, thus E and IE will. each tend to produce a voltage in the ma chine F equal to the voltage across their respective motors. Similarly the winding L will produce an electro-motive force equal to the difference between the effect of K and the effect of H. Now it is evident that the voltage across the mains is equal to the sum ol the Voltage across the motors plus the voltage across the machine 1. Consequently if the effect of K is chosen to be such as it acting by itself it would produce in the mechine an electro-motive' force equal and opposite to that of the mains, then the effect of the resultant between this part K and the sum of the parts E and E would be to pro-- duce in the machine F a voltage across its terminals always equal to the voltage ap plied thereto; while the part H serves for the purpose of balancing the voltage drop in the regulator F. Consequently this rangement ot' windings is equivalent to that which would produce the characteristics in Figure l. C 13 represents the effect of H which of course would be represented by a line parallel to and removed. :fro1n the line Bin the direction o1"? A O; O B being the characteristic of the machine F and also the characteristic of the resultant excitation of E, E and K. Due to this the machine l will maintain the current constant "while working below the limits of saturation. The

slight modification in the excitations oi E and B would produce a diagram corresponding to Figure 3 while similarly the machine would work in a saturated portion of its characteristic corresponding to the diagram ct Figure The value of the part H will inliuenre the value of the predetermined on rent. I

llaturally the winding ill E could be replaced by a sinewinding placed across the terminals or! one of the motors and giving a capable of sending a current through the winding (4, b, which i at all times proportional to the excitation applied to it. This machine will only be of a re y small size as the energ', which it has to produce. is very small. Its excitation takes the form of two windings c and it. e is directly connected :trIOSS the terminals of the machine F, and oi? such value that its elfect on the system is to produce an electromotive force in machine l equal to that across its terminals I when working in the straight portion of its characteristic, while the winding it is con-- neiicted to a source of constant current of fixed value. this'means seeing that the machine i very small the inductance oi the winding will. be much less than would be the case it the an. "my dynamo had not been substituted. The advantage of this is of course that the'maehine readily respond: to changes of voltage in the system. It is therefore very stable.

may be mentioned that this machine could be advantageously employed in mul tiple unit traction systems.

in order to increase the stability and to further ensure the constancy of the current the winding 7,- can be replaced by two opposing windings. through one of which passes a vonstant current while through the other passes the current traversing the armature oi the machine l For ostablishin .nralcing conditions the field winding or the traction motors may be shu ted by an ohmic resistance. ltwill be reauily seen that it this resis -ince be left in circuit during the whole period of ln'alringgj. it will have a stabilizing effect. ln fact, any sudden increase of the current will affect only the ohmic resistance shunting the lield coils, without sensibly modifying the current lll) produced by passing through these latter, but it will'be understood that this stabilizing effect will be the greater according as the value of the resistance is small relative to that of the field coils of the traction motors. This circumstance would lead to the shunting of an important part of the field current of the motors in order to render the stabilizing means suiliciently effective, and accordingly theresisting torque would be decreased more than is desirable. i v i In the following discussion the idea just n'ientioned is further developed, but in a manner which avoids the disadvantage pointed out. I

On Figure 6 of the accompanying drawings X Y is the circuit of the traction motors. m m, are field windings of these motors. R is an auxiliary dynamo running at constant speed, being, "for instance, driven by the shaft of the regulator. '1 and 2 are switches which permit oi. the cutting out or putting into circuit or the auxiliary machine R and the winding A B respectively.

- During the braking period with which we are now concerned, the swltch 1 is closed and the swltch 2 is'open.

The auxiliary dynamo B may have both excitations A B and a Z) in action simultane ously, or each one of these may be acting alone, and accordingly three different methods of working are possible. 'ltfis first assumed that the independent excitation. (L b is acting alone. In this case the Switch 2 is closed. l

T his excitation at Z) is adjusted, for instance so that when the working conditions of the machine have been established the 'E. M. F. oi the machine tential difference between the points (7 l) the passage of the current through the field windings m 972. This E. M. F. is opposed to the passage of the current through the armature of the machine P- and in. the case of sudden variations of current the arrangement behaves practically as if the field windings m m were actually shunted by the ohmic resistance vin this armature, which has very small resistance and practically negligible self-induction.

It the excitation A B actsalone and it this is also adjusted so that when the working conditions of the machine are established the li l. F. of the auxiliary machine R balances the difference of potential between the points C D, this .machine will. act in a manner analogous to that previously indicated for sudden variations of current.

it is clear that it the machine liiworks within the limits where its magnetic circuit is not saturated. the balance established between the E. M. F. of the machine It and .the potential diiterence between the points C D for given conditions will subsist whatever may he the strength of the current.

halances the po lVithin the prescribed limits this arrange- ,ment permits of preserving for the motors adjusted so that the difference of their ampere-turns induces for iven conditions i of working the same E. M F. in the machine R as under the preceding conditions.

It is seen that in this last case the machine R, in place. of serving simply as a buffer for thesudden changes, also acts as a stabilizer for all chance variations of current;

It for some accidental reason the current sent out by the traction motors tends to fall below the value determined for it, the E. M. F. of the dynamo R increases. The current in the field windings m 'm also in creases, which results in the increase of the current sent out into the line. If the current tendsto increase the inverse effect is produced. T g

In the preceding discussion it has been assumed that the'E. M. F. of the machine R balances the voltage between C D, but it will. he understood that in place of having exact balance, any desired degree of shunt- .ing OTftllE field current could be obtained by adjusting the E. M. F. of the'machine R to 'a suitable value.

Obviously the arrangements above men'- t'ioned can be utilized if desired during the starting oeriod. f Another method of excitation of the auxiliary dynamo R is illustrated in Figure 7 the accompanying drawings. On this drawing X Y is the circuit of the traction motors. m, m, are their field windings. R is the auxiliary dynamo. A B and a b are the excitation windings of this auxiliary dynamo. A is connected to the terminal of the machine F (see Figure 8). The corresponding excitation accordingly has a value which is variable in magnitude and direction. The other winding a 6 produces an excitation of constant value and may be, 'i

for instance, connected to the line. These two windings are arranged so that they act in the same sense "for a small motor voltage. I is a switch providing for the cuttin out or putting into operation or this auxhiarv machineR. p i From the point vie-wot stability the result of this arrangement prz'tctically the same as if the field windings of the traction motors were actually shuntedby the resistance of the armature oflthe mac'hineR, since the voltage of this machine R will not mate rially increase when sudden increase of the main current takes place.

Further, if the resistance of the armature ol the dynamo R be neglected (it is comparatively very small and its action can be cminter-acted, for instance, by compound excitation or by a suitable displacement of the brushes) the excitation current of the trac ti on motors is practically independent of. the main current and depends solely upon the voltage of the terminals of the machine F that is to say, upon the speed of the motors.

It will be understood that if the speed of the traction motors at which braking is commenced is increased, the voltage at the terminals of these motors at the commence ment of the braking period will also increase, although their excitation current diminishes and consequently the excitation current would only become zero for an infinite speed of the motors. On the other hand, it is evident that this excitation current is a maximum when the motors are stopped.

Under these conditions 1st. Since the excitation of the dynamo R cannot become zero, the voltage at the terminals of the machine F, and consequently that of the traction motors, is limited.

2nd. The excitation of the traction motors being independent of the current, the value of this latter can be separately adjusted by means of the excitation of the machine F, permitting the easy realization of several degrees oi braking action.

3rd. The stability of this latter is delinitely ensured tor sudden variations of the main current are without effect on the voltage of the dynamo R.

Further, if an accidental increase of the voltage of the motors should be produced, it would result in a diminution oi? the voltage of the auxiliary machine R which would ensure the stabilization of the braking conditions.

It has just been pointed out how the excitation A B of the auxiliary dynamo R permits, by its variations the limitation oi. the difference of potential at the terminals of the traction motors for increasing speeds at the moment of braking, and that the excitation of the traction motors is a maximum at the stoppage.

Now it may be desired to maintain the excitation current of the traction motors ap proximately constant below a given speed. For instance, it it is desired to obtain a practically constant braking torque. In order to produce this result it is only necessary to suitably select the magnetization characteristics of the dynamo B, so that for low speeds this dynamo works with a saturated mag netic circuit.

It will readily be seen that the arrangement which has just been described can be utilized not only during braking, but also during the starting period by connecting the excitation windings of the machine R so as to act in a suitable sense.

()n the other hand. since the main current through the armatures of the traction motors has no appreciable influence on the strei'igth of the current through the field windings of these motors, the circuits oi these windings m, and m and of the dynamo R can be isolated, that is to say, separated from the principal circuit X Y, but then the auxiliary machine R would require to have a greater power.

It in such a case the auxiliary machine ll be employed for stt and tor bral'ing, it would be possible, by a judicious choi 1 oi the characteristics oi the machine li'irming the automatic regulator group inchiding the dynamo R, to maintain for the traction motors their series characteristics, that to say, to cause their excitation current to be approximately equal to the main current whatever may be the speed. Instead of this, other suitable working characteristics can be given to them.

Further, under the same circumstances, it will be noted that the direction and the magnitude of the current through the armatures of the traction motors are determined by the excitations of the machine F that the direction and magnitude of the current pass ing through the field windings oi the traction motors are determined by the excitations of the auxiliary machine 1t. Consequently all the methods of connection and speeds of running which it is desired to realize as well as starting up and braking, can be obtained by acting upon excitation currents of comparatively small values. This remarlr applies particularly to the method of control with multiple motor units. It permits ot the suppressing of several of the control devices, such as contactors or reversing switches, and consequently permits ot' the production oi. a much simplified equipment.

A complete system embodying the arrangements described with reference to Figures 5 and 7 is illustrated in Figure 8 as applied to a traction system oi two series motors M, M Here we have series motors M, M with their corresponding field windings 722, m the regulating machine F with l'irushes e, 6 and with winding U driven at constant speed by the shunt wound motor l1 Across the field windings m, 9/1,, is placed the auxiliary dynamo It with its windings All. (/1). while across the winding l is the small auxiliaiy dynamo with it windings e and 71.. Switches are provided numbered 1, 2, 3, l, 6, 12, 34-, 15 and 16 for switching the various parts in and out of circuit. Switch 3 is a change-over switch I which can be used both to rev the field winding of the motors and to switch them in and out of circuit. Regulating resistances 8 ot the regulator and 9 are, provided for regulating the conthe current in the winding 72/.

due to accelerationof the motors.

versmg the current for bra-king purposes all stant current through the windings ab of the auxiliary machine R and the winding it of the auxiliarymachine hese are shown across the mains although any method of regulation which would givenconstant current could be adopted, such as cells. Reversing switch 16 is provided for reversing I The exact method of working need hardly be gone into as this has been discussed separately above. The operation of the device will be briefly explained. For normal starting all the switches 1, 2, 4L, 6, 15, 12, 14 will be closed. Regulating resistances 8 and 9 are also adjusted as desired and the switches 16 and 3 in the correct position for starting. Current now flows through the motors M and M their field windings 022,, m and the armature of the machine F, in series,'the current being regulated to a given value'determined by the adjustments above mentioned. The winding 6 is energized due to the difference oi pot-em tial between the armatures of the motors M, and M ,-wh le the field winding B 1S energized due to thepotential across the ter- I minals 6 -6 I As the motors M, speed up, the increase in their counter electrome- Ztive force tends to decrease the effect of the winding 6 on the dynamo f with a consequent decrease in the field strength of the regulator F and a decrease in its voltage, which in turn reduces the opposition to the flow of current in a proper ion to compensate for the increased counter electromotive "force For rethat is necessary is to switch overthe switches 3 andlG, The motors now act as generators in the. well known manner, their output, and consequently the mechanical load or braking effect, being regulated by the opposing effect of the regulator F whose electromotive force is now reversed. The provision of the small auxiliary dynamo and all the low inductance in the circuits of the regulator f insures an almost immediate response of the regulator to rapid changes of current and thus avoids all dangerous curt Claims.

- 1. electrical system comprising in combination a motor, mains, connections between the terminals of said motor and said mains, I a dynamo electr c machine, adapted to work in the saturated portion of its characteristic, inserted in said connections, and means for driving said machine at constant speed, and means whereby said machine is acted upon by a flux Whiehis theresultant oftwo com ponent factors, one of which acting alone would generate a constant electromotive force, and the other acting alone would generate an electromotive force nearly equal 2. A series-parallel and regenerative system comprising in combination two motors, mains, connections adapted; to join one terminal of each motor to the co'ri.'es )ond ing main, a dynamo electric machine having each of its terminals connected to the other terminals of said motors, and means for driving said machine at constantspeed, and means whereby said machine is acted upon by a flux which is the resultant of two component factors, one of which acting alone would generate a constant, E. M. F. and the other acting alone would generate an E. M. F. nearly equal and proportional to the voltage across the terminals of said machine, when said machine is working in the nonsaturated portion of its characteristic.

3. An electrical system comprising in combination a motor,mains,"connections between the terminals of saidmotor and said mains, a dynamo electric machine, means to drive said dynamo electric machine at constant speed, an excitation winding connected to asource ofconstant current and adapted to produce in said'dynamo electric machine it acting alone a constant electro -motive force, a second excitation winding connected across part of the motor circuit, the two windings being adapted to produce in said dynar'no electric machine an electromoti've force nearly equal and proportional to the electrornotive force across the dynamo electric mains, connections between the terminals,

of said motors and said mains, a dynamo electric machine, means to drive said dynamo electric machine at constant speed, an excitation winding connected to source of constant current and adapted to produce in said dynamo electric machine if acting alone a constant electromotive force, a second excitation winding connected across part oi the motor circu t, the two windings being adapted to produce in said dynamo electric machine an electromotive force nearly equal and-proportional to the electro-motive force across the dynamo electric machine. 7

5; An electrical systemcomprising in combination a motor, mains, connections between the terminals of said motor and said mains,

a dynamo electric machine, means to; drive said machine at constant speed, an auxiliary dynamo electric machine work ng 111 the r chsaturated portion of its characteristic, means. to produce a flux in sa d mach ne which is the component of two auxiliary fluxes, one of which is constant and the other proportional to the Voltage across the terminals characteristic, means to of said first mentioned machine, and connections between the terminals of said auxiliary machine and the field winding oi. said lii'st named machine.

6. An electrical system comprising in combination a motor, mains, connections between the terminals of said motor and said mains, a dynamo electric machine, means to drive said machine at constant speed, an auxiliary dynamo electric machine working in the non saturated portion of its charac teristic, means to )roduce a flux in said auxiliary machine w iich is the component of two fluxes, one of which is constant and the other proportional to, and of such value as to produce in said first named machine an E. M. F. nearly equal to the voltage across I the terminals of said auxiliary machine, and

connections between the terminals of said auxiliary machine and the field winding of said first named machine.

7. An electrical system comprising in combination a motor, mains, connections between the terminals of said motor and said mains, a dynamo electric machine, a field winding on said dynamo electric machine having few turns and small sellf induction, means to drive said machine at constant speed, an auxiliary dynamoelectric machine working in the non saturated portion of its produce a flux in said auxiliary machine which is the component of two fluxes, one of which is constant and the other proportional. to the voltage across the terminals of said machine, and connections between the terminals of said auxiliarymachine and the field winding of said first named machine.

8. An electrical system comprising in combination a motor, mains, connections between the terminals of said motor and said mains, rotary apparatus for supplying constant current and an auxiliary dynamo connected. across the field winding of said motor generating an E. M. 1*. equal to the normal voltage across said winding.

9. An electrical system comprising in combination a traction system of series motors, mains, connections between the terminals of said motors and said mains, rotary apparatus for supplying constant current, and an auxiliary dynamo connected across the field winding of said motors generating an E. M. F. equal to the normal voltage across said winding.

10. An electrical system comprising in combination a motor, mains, connections between the terminals of said motor and said mains, rotary apparatus for supplying constant current, and an auxiliary dynamo connected across the field winding of said motor. said auxiliary dynamo having an excitation the value of which varies with the voltage of said. rotary apparatus.

11. An electrical system comprising in 'nected across the field winding combination a motor, mains, connections be tween the terminals of said motor and said mains, rotary apparatus for supplying constant current, and an auxiliary dynamo consaid inotor, said auxiliary dynamo having an excitationv which is the con'iponent of two excitations, one of which is constant and the other proportional to the voltage across said rotary apparatus.

12. An electrical ystem comprising in combination a motor, a field winding on said motor, mains, connections between the tern'iinals of said motor and said mains, rotary apparatus for supplying constant current, and an auxiliary dynamo connectedv across the motor field 'windii'ig and having an excitation proportional. to the voltage acros said rotary apparatus.

l2. An electrical system con'qn'ising in combination a traction system ot series inotors, mains, connections between the terminals of said motors and said mains, rotary apparatus tor supplying constant current. and an auxiliary dynamo connected across the field winding ol' said n'xotor, said auxiliary dynamo l'iaving an excitation, the value of which varies with the voltage across saidv rotary apparatus.

An electrical system comprising in combination a traction system of series motors, mains connections between the teri'ninals oi said motor and said mains, rotary apparatus for supplying constant current, and. an auxiliary dynamo connected across the field winding of said motor, said aux- .iliary dynamo having an excitation which is the component of two excitations, one of which is constant and the other proportional to the voltage across said rotary apparatus.

'55. An electrical system comprising in combination a traction system of? series motors. mains, connections between the terminals of said motor and said mains, rotary apparatus for supplying constant current, and an auxiliary dynamo connected across the field winding of said motor, and having an excitation proportional to the current through said motor. 0 I

16. An electrical system comprising in combination a motor, mains, connections between the terminals of said motor and said mains, a dynamo electric machine, means to drive said machine at constant speed, an auxiliary dynamo electric machine, and means whereby said machine is acted upon by two fluxes, one of which is constant and the other proportional to the voltage across the terminals of said first named machine, connections between the terminals of said auxiliary machine and the field windin of said first named machine, the said auxiliary machine working in the non-saturated portion of its characteristic, an auxiliary dynamo across the field winding of said motor generating an E. M. F. equal to the normal voltage across said winding.

17. A series-parallel and regenerative system comprising in combination two motors, mains, connections adapted to join one terminal of each motor to the corresponding main, a dynamo electric machine, the ter- 'minals of said machine beingconnected'to the other terminals 01": said motors, exciting windings adapted to produce electromotive forces in said dynamo electric machine, and means for supplying one of which with constant current, and the other with current proportional to the E. M. F. across part of the motor circuit.

18. An electrical system comprising in combination a motor, mains, connections between the terminals of said motor and said mains, rotary apparatus comprising means for generatingtwo electromotive forces, one of constant value and the other nearly equal and, proportional to the voltage across the terminals of said rotary apparatus, and an auxiliary dynamo across the field winding oi said motor, generating an E. M. F. equal to the normal E. M. Fpacross the field winding.

19. An electrical system comprising in combination a traction system of series motors, mains, connections between the terminals of said motor and said mains, ro-

tary apparatus comprising means for gen-' erating two E. M. F.s one of constant value and the other nearly equal and proportional to the voltage across the terminals of said rotary apparatus, and an auxiliary dynamo across the field Winding of said motor, generating an E. M. F. equal to the normal E. M. F. across the field winding.

20. An electrical system comprising in combination a traction system of series motors, mains, connections betweenthe terminals of said motors and said mains, rotary apparatus comprising means for generating two E. M. Fs, one of constant value and the other nearly equal and proportional to the voltage across the terminals of said rotary apparatus, an auxiliary dynamo across the-field winding of said motorsgencrating an E. M. F. equal to the normal E. M. F. across the field winding, two field windings on said dynamo electric machine, one having constant current through it and the other proportional to the voltage across the terminals of said rotary apparatus 21. An electrical system comprising in combination a motor, mains, connections between the terminals of said motor and said mains, a dynamo electric machine, means to drive said machine at constant speed, an auxiliary dynamo electric machine working in a non-saturated portion of its characteristic, an excitation winding connected to a source of constant current and adapted to produce in said dynamo electric machine if acting alone a constant electromotive force, a second excitation winding connected across part of the motor circuit, p the two windings being adapted to produce in'said dynamo electric machine an electromotive force nearly equal and proportional to the electromotive force across the dynamo electric machine.

In witness whereof, I have hereunto signed my name this. 21st day of March 1913, in the presence, of two subscribing witnesses.

FERNAND CUMONT.

Witnesses:

BARTLEY F. Yosr,

Anrnonsn MEJEAN. 

